1. Field of the Invention
This invention relates to increasing the concentration of a dissolved gas in a quantity of liquid, and more particularly, to oxygenation of controlled volumes of aqueous fluids.
2. Description of the Prior Art
It is desirable for certain purposes to increase the concentration of dissolved gases within bodies of liquid. For example, it is advantageous to raise the concentration of dissolved oxygen in a body of sewage so that sewage treatment processes are accelerated. Such an application may require increased dissolution of air within a quantity of liquid for subsequent deposition in the body of sewage, or it may be desirable to dissolve molecular oxygen within a quantity of liquid and to thereafter mix the oxygen rich mixture into the body of sewage. Dissolution of air or oxygen into a body of liquid is accomplished at a relatively slow rate at atmospheric pressure and dissolution at superatmospheric pressure is therefore often attempted to accelerate the rate of dissolution. When molecular oxygen is utilized for dissolution into a liquid, loss of the oxygen which either does not enter into solution or comes out of solution prior to utilization of the oxygenated solution poses a cost problem since the molecular oxygen is a relatively expensive gas.
U.S. Pat. No. 3,926,588 issued to Speece discloses a gas transfer device within which absorption in a liquid of a gas from a pressurized source may be enhanced by pressurizing the gas-liquid mixture. The liquid is introduced through the top of a conical shaped chamber at a velocity exceeding the buoyant velocity of the bubbles of gas which are injected by a gas injector within the chamber. This results in an accumulation of bubbles at a stagnation zone within the chamber because the gasified liquid emerges from the bottom of the chamber at a velocity which is lower than the buoyant velocity of the gas bubbles. The accumulated gas in the stagnation zone which is not absorbed by the liquid is thereafter vented from the chamber and lost.
U.S. Pat. No. 3,799,511 issued to Svantesson discloses a device for mixing gas and liquid within a vessel which is located beneath the surface of a body of liquid by pumping air and liquid downwardly through a conduit to enter the vessel. The velocity of downward flow is sufficient to carry the air downward with the liquid. The mixture of gas and liquid is discharged from the lower open end of the conduit at a region near the bottom of the vessel. As the mixture of gas and liquid ascends upward within the vessel, some of the air is dissolved in the liquid. The air-liquid mixture is subjected to a superatmospheric pressure dependent upon the depth within the liquid body at which the vessel is placed. The gas-liquid mixture is retained within the vessel for a period of time which is sufficient to allow air to dissolve into the liquid within the vessel while out of physical contact with the main body of liquid outside the vessel. Excess gas within the vessel is continuously vented through a pipe attached thereto and is not recovered.
U.S. Pat. No. 3,530,990 issued to Grimshaw describes a sparger which includes a cylindrical container having a compressed air inlet and a vent at the top thereof. A liquid is introduced into the container together with compressed air until the pressure within the container reaches a predetermined level. At the predetermined pressure level a relief valve opens which allows continued introduction of pressurized air to force the aerated liquid from the container. Excess air is thereafter vented from the top of the container and lost.
It is therefore clear that a device for enhancing the concentration of a gas in solution in a quantity of liquid is desirable wherein that portion of the gas which either does not go into solution or which comes out of solution is recovered to be thereafter available for dissolution in another quantity of liquid.